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Discussion Starter #1
So I’m new here and if this thread isn’t in the right place let me know, thanks! So my ‘02 zetec zx3 has the cooling issue that these cars seem to have. The issue I have is that when the car is revved and the engine gets really hot the coolant overheats and bursts out of the smaller reservoir. Sitting in traffic is ok for short periods of time and normal driving is fine, it doesn’t really overheat. The funny thing is that I have never heard the cooling fans kick in recently. Even with the ac on the fan doesn’t kick into low speed. Crawling through the forums I’m pretty sure I’ve nailed every possible attempt at fixing to no avail. I replaced the thermostat, the head temperature sensor, the resistor between the fans, gone through the wiring, checked and doubled checked the relays, jumped the relays to check if voltage is there (which it is), and I’ve even disconnected the fans and ran the fans on an external 12v source. Still no cooling fans. My next question is this: the ac does not blow cold air now which I’ve noticed since it got hot out by me. Could the no fan problem be due to a compressor that has no oil in the system? From what I understand the ac circuits and cooling fan circuits are related. I’m thinking there might be an error in that circuit causing the cooling fans not to turn on. My dad thinks the PCM is bad and just isn’t sending a signal to turn to the fans on even if the temperature gets hot. To top this all off I’ve used a mechanics scan tool to find the special test to turn the high speed and low speed fans on which I can command to do so through the scan tool. I hear the relays click and the fans come on. That’s the only way I’ve been able to get the fans to kick on. Any and all help would be greatly appreciated and I apologize for the length of this post.
Thanks!
 

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Thats What She Said
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Welcome to the forum.

Spaces and paragraphs help with reading the posts to know whats going on.

If the AC is on you should always have high speed fans going. You would want to check the relays are working correctly. fuses are good. There is also a diode on the AC compressors clutch to prevent back EMF from hurting electroncis.

Are you able to tell if the AC Compressors clutch is engaging?

Have you put 12V directly to the fans to see if the fans work with voltage directly powered to them? could have bad fans or a short or something in the fans.

To tell if the signal is getting to the fans check the relays. Thats what a relay does, it allows a low power signal to energize a switch to allow for a high power / current path. So is the relay getting a signal? are you able to read the electrical diagrams in a repair manual?
 

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Discussion Starter #3
Sorry about the grammatical errors, just getting used to the format of this forum.
So I’ve checked that the relay is indeed getting power at the junction box and jumped posts to put power to the fans in which I have been able to turn the fans on. I’ve checked the relays and the relays are good. (At this point I guess I’ll just replace the relays for the whole $20 it’ll cost me lol)

I have run external 12v to the fans to confirm that they run.

I have not checked the issues at the ac as of yet. So no I do not know nor am I sure if the clutch for the ac is engaging.

I am not aware of the diode on the ac compressor. Where is that located and would it directly affect fan function?
 

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2006 ZX5 2.0, 2004 ZX3 SVT EE. 2004 ZX3 SVT
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Welcome. I have a 2002 with the same problem. Instead of throwing parts at it. Verify signal to relay. The high beam relay is the same as the fans. Swap them out and see if you now have fans. If not you need to check for a signal at the relay from the computer. You need an illuminated test light. I wired the fans to a switch as I was never able to resolve this before giving the car to my son. Please repost if you resolve this so you can help I others.
 

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Thats What She Said
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Not sure the internal ECU logics but the diode is in line for the AC compressor. if thats an open and never turns on or engages I am not sure if the fans would turn on becuase the AC is not really on.

We all make errors. Spaces and paragraphs ever few lines just make it easier to read and follow than a large block of text.

when you say over heat what is over heat and how are you measuring it? the fans dont turn on until some 220F and then 240F or something like those numbers. a bad cap on the degass (the coolant overflow) canister can cause things to over heat also. You have it filled to the correct level when at room temp? no air bubbles? All the hoses are connected in the correct location?

You can have 12V to the relay There is a input and a output and a control. when the control voltage is present (could be 5V or 12V or 3.3V) the relay coil engages and passes the voltage through. so you have varrified that there is both power (from the battery) to the relay contact, and the control line has votlage when the the MAX AC line is enabled and goes off when turned off? if thats what you are measuring then the relay is bad.
 

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Discussion Starter #6
Welcome. I have a 2002 with the same problem. Instead of throwing parts at it. Verify signal to relay. The high beam relay is the same as the fans. Swap them out and see if you now have fans. If not you need to check for a signal at the relay from the computer. You need an illuminated test light. I wired the fans to a switch as I was never able to resolve this before giving the car to my son. Please repost if you resolve this so you can help I others.

When you wired the fans to a separate switch what gauge wire did you use and where did you branch the switch out of?

My concern is that if I have a separate switch for the fans the draw is going to cause my battery to die and load through the wires may melt them.
 

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Discussion Starter #7
Not sure the internal ECU logics but the diode is in line for the AC compressor. if thats an open and never turns on or engages I am not sure if the fans would turn on becuase the AC is not really on.

We all make errors. Spaces and paragraphs ever few lines just make it easier to read and follow than a large block of text.

when you say over heat what is over heat and how are you measuring it? the fans dont turn on until some 220F and then 240F or something like those numbers. a bad cap on the degass (the coolant overflow) canister can cause things to over heat also. You have it filled to the correct level when at room temp? no air bubbles? All the hoses are connected in the correct location?

You can have 12V to the relay There is a input and a output and a control. when the control voltage is present (could be 5V or 12V or 3.3V) the relay coil engages and passes the voltage through. so you have varrified that there is both power (from the battery) to the relay contact, and the control line has votlage when the the MAX AC line is enabled and goes off when turned off? if thats what you are measuring then the relay is bad.
I have used the test mode trick and setting the ecu to read temperatures where the odometer display is. I have confirmed that the engine is hot when fan the fans should engage.

I definitely have filled the coolant to the proper level without air bubbles and perhaps the cap to the reservoir is a good piece to test and possibly replace. There have been issues where I sit in traffic for too long and the coolant boils in the reservoir and evaporates without the fans ever engaging.

I have not verified the above concerning voltage when the max ac button is on. Do you happen to know the post numbers on the relay for the fans where there should be control, input and output voltages?

For the ac I’ll try a cheap recharge kit and see if I can solve the issue on that end.
 

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I used 6 gauge wire and a relay rated for 60 amps. I wired the main power to the battery for the relay and fan but used a switch wired off of the fuse box that was only hot with the key on. Do not recharge the ac yourself. Bad idea.
 

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Thats What She Said
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I dont have a wire diagram infront of me to know the pins.

The relays usualy show a diagram of what the internals are

https://www.explainthatstuff.com/howrelayswork.html

In the link provided the ECU is providing the voltatge to #1 and #2 (or #3 for the light blub animation) is hooked to the battery through a fuse.

This is what you want to do so you are not running 6 AWG wire into the cabin. This is why they use relays, use low power logic and switches to control high power devices.

Edit: A Fun note is you can do this with solid state FET's also and is fun to try to do but beyond what your trying to solve, but a solid state switch that removed the relays is also somehting someone can do.
 
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